The use of optical rotating joints (ORJs), also known as fibre optic rotary joints (FORJs), for transmission of an optical signal in a fibre-optic cable across an interface between two physical entities, where at least one of the physical entities is rotating, is known. One type of ORJ is a single channel single-mode ORJ, i.e. one in which optical signals are transmitted across the rotating interface from one fixed single-mode optical fibre to one rotating single-mode optical fibre.
In some applications of ORJs, optical plural signals or channels are multiplexed, for example by time-division multiplexing or wavelength-division multiplexing multiple signals on a single optical fibre or channel.
Examples of the above arrangements are described, for example, in a document which was retrieved from the Internet and is an Application Note made available by MOOG Components Group of Moog, Inc., identified as “Document Number 231”, entitled “Video/Data Transmission and Distribution in Turreted Vehicles with Situational Awareness Systems”, and authored by Glenn Dorsey. The document gives a website www.moog.com/components and an email address mcg@moog.com.
Conventionally, in applications where ORJs are used, redundancy is introduced to alleviate the effects of failure of the ORJ. In many ORJ arrangements, redundancy is conventionally provided at a given physical rotational interface by providing alternative ORJs through which the signals may be diverted, as this is considered relatively pressing due to the perceived mechanical vulnerability of the moving parts in an ORJ.
Quite separate from the field of ORJs, optical circulators are known. For example, the Thorlabs (trademark) website at
http://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=373
provides details of commercially available optical circulators, which may be obtained for example from Thorlabs, LTD., 1 Saint Thomas Place, Ely, Cambridgeshire CB7 4EX, UK.
Quite separate from the field of ORJs, optical switching is known. Examples of optical switching are described, for example, the Dicon Fiberoptics Inc. (trademark) website at
http://www.diconfiberoptics.com/products/prd_switches.php
provides details of commercially available optical switches, which may be obtained for example from Dicon Fiberoptics Inc., 1689 Regatta Blvd., Richmond, Calif. 94804, USA. For example available is a range of optical switches that have a single optical fibre input and up to eight switched outputs. More generally, optical switches are available based on mechanical or electro-optic switching technologies.